Internet Protocol (IP) telephone systems, IP video conference systems, or other similar systems, in which sound data and picture data are transmitted (in a form of packet communication) using network circuits, have adopted the User Datagram Protocol (UDP) communication, because such systems need the securing of continuous communication band.
The UDP communication however will lose excess packets if communication information is inputted beyond the transmission capacity of transmission lines.
In a video conference system working on a packet communication, loss of some of picture data packets will cause drop frame of screen and loss of some of sound data packets will cause speech interruption making sound harsh.
To prevent drawback like that, a packet communication system has been proposed (Japanese Patent Application Laid-open, No. 2004-297265). The proposed system has routers on transmission lines for selection of a circuit from among plural transmission routes, wherein the routers select a transmission route according to the transmission delay time of packets.